J. Ruschel¹, J. Glaab¹, N. Susilo², S. Hagedorn¹, S. Walde¹, E. Ziffer², H.K. Cho¹, N. Lobo Ploch¹, T. Wernicke², M. Weyers¹, S. Einfeldt¹, and M. Kneissl^1,2

Published in:

Appl. Phys. Lett., vol. 117, no. 24, pp. 241104 (2020).

Abstract:

The impact of different AlN/sapphire template technologies [i.e., planar, epitaxial lateral overgrown (ELO), and high temperature annealed sputtered ELO] is studied with respect to the operation-induced degradation of 265 nm UVC LEDs. UVC LEDs with identical heterostructures were grown on templates providing different threading dislocation densities in the range of 0.8×10⁹cm^-2 to 5.8×10⁹cm^-2. A long-term stress experiment was performed on batches of LEDs, which were operated at a direct current of 200 mA corresponding to a current density of 60 A/cm² and at a heat sink temperature of 20°C. The UVC LEDs on templates with lower threading dislocation densities were found to provide a higher optical power and to degrade slower during 2000 h of operation. The experiment demonstrates an extrapolated L70 lifetime of more than 10 000 h for the high temperature annealed sputtered ELO technology. The results suggest that degradation is caused by operation-induced activation of defects whose density scales with the dislocation density.

Topics:

Ultrawide Bandgap Semiconductors, Heterostructures, Emission spectroscopy, Crystallographic defects, Epitaxy, Quantum wells, Semiconductor device fabrication

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